1. Field of the Invention
This invention relates to a process for hydrogenating conjugated diene polymers having hydroxyl or carboxyl groups, or groups derived from the carboxyl group at high hydrogenation rates without damaging the groups present in the conjugated diene polymers.
2. Description of the Related Art
Among conjugated diene polymers having hydroxyl or carboxyl groups, or groups derived from the carboxyl group (which polymer may be hereinafter referred to simply as "modified polymer" and which group may be referred to simply as "substituent"), conjugated diene polymers having a substituent at one or both ends are useful for reacting with diisocyanate compounds to form moldings with a high resistance to hydrolysis. Alternatively, conjugated diene polymers having substituents in the molecular chain exhibit good rubber elasticity and can be cured by means of sulfur or peroxides. Moreover, the polymers may undergo various modifications depending upon the type of functional group in the polymers. As will be appreciated from the above, it is known that a variety of functions can be imparted to the conjugated diene polymers by introducing certain functional groups into the polymers. The carbon-carbon double bond in the conjugated diene polymer serves as an important reaction site when the functional groups are introduced into the polymer, but will cause the weatherability, light resistance and heat resistance of the resultant modified polymer to lower. In order to improve the weatherability, light resistance and heat resistance, it is considered to hydrogenate the carbon-carbon double bond in the presence of a catalyst.
Known catalysts for the hydrogenation used for the hydrogenation reaction of the carbon-carbon double bond are those of nickel, palladium, ruthenium and the like (Japanese Laid-open Patent Application Nos. 50--90694 and 52--111992 and United States Patent No. 4107225). However, when modified polymers are hydrogenated by the use of these catalysts, there are encountered problems in that the hydrogenation reaction does not proceed at all by the presence of the substituents, the hydrogenation rate lowers considerably, or the chemical structure of the substituent changes or the substituent is eliminated from the modified polymer. Since the palladium or ruthenium catalyst is expensive, its application to the hydrogenation reaction of modified polymers brings about an increase of production costs, thus being disadvantageous from the industrial viewpoint.
An object of the present invention is to provide a process for the hydrogenation of modified polymers which solve the prior-art problems.
Another object of the invention is to provide a process for the hydrogenation of modified polymers which has a high hydrogenation rate and in which substituents present in the modified polymers are not damaged.
Other objects, features and advantages of the invention will become apparent from the following description.